1. Field of the Invention
This invention relates to power steering apparatus, and more particularly to a type thereof in which a torque detecting device detects torque in a noncontacting manner by converting a twist of an angular deformation creating mechanism such as a torsion bar into a variation of an electric capacity.
2. Description of Prior Art
Heretofore power steering apparatus utilizing hydraulic, pneumatic and electric power have been widely known. However, on a vehicle such as an electric lift, electric motor car and the like wherein an electric motor is utilized as its prime-mover, electric steering apparatus is used advantageously for eliminating the installation of a hydraulic pump or else separately. For instance, Japanese Patent Laid-Open No. 190,240/1982 discloses a technique in which a member creating a relative displacement is provided between the input shaft and the output shaft of the power steering apparatus, and the relative displacement is detected from the excitation of an inductor. However, since the prior art utilizes a frequency near the resonant frequency of a tank circuit, a high precision frequency selectivity is required for the oscillator. Furthermore, a number of mechanical and electrical parts are used in the detector, and hence the assembling of the detector becomes troublesome. In addition, the detector has required frequent maintenance because of fatigue or else, thus restricting general use of the prior art apparatus for ordinary vehicles.